Recommendation for iPhone-based group task management

I have a group of four people that want to assign “to-do’s” to each other (it comes into a central dispatcher, and then gets assigned to one of three people).

The dispatcher wants to get notified when the person completes the to-do, and wants to see what tasks are outstanding. Everybody has an iPhone.

Any suggestions on what can be used that is reasonably priced? Would a dedicated iPhone app be better otherwise, I can install something web-based like Wordpress.

Maybe asana?

Interesting, I had never heard of it before, but it looks like it might do the trick!